The field of dolls, more specifically, the field of walking dolls.
There have been walking dolls based on complicated clockwork mechanisms since the renaissance, with increasing popularity in the eighteenth and nineteenth centuries. Dolls with complicated mechanisms could only be afforded by the upper class, as these mechanisms were hand constructed, fairly delicate curios, and more works of kinetic art than utilitarian toys for average people. With the advent of plastic and the cheaper manufacturing and mass production of the twentieth century, dolls as toys for the average person of average means became more available, and ultimately ubiquitous. Many of these dolls were combinations of plastic and plush, some more realistic than others in their anthropomorphism of the human form.
As with all toys, the goal has always been the creation of a product with the most play value for the least money. The present doll strikes that balance with a unique mechanism that marries simplicity with human interaction to produce a dramatic walking action and play pattern coupled with high perceived value.